Caloric vestibular stimulation (“CVS”) has long been known as a diagnostic procedure for testing the function of the vestibular system. In the traditional hospital setting, water or air caloric tests are used to assess levels of consciousness during acute or chronic brain injury. The brain injury may be due to head trauma or a central nervous system event such as a stroke. Other brain injuries occur in the presence of metabolic abnormalities (e.g., kidney disease, diabetes), seizures, or toxic levels of controlled substances or alcohol.
More recently, CVS has been applied to other purposes. A general review of some successful experimental uses of CVS is given in Miller and Ngo, Acta Neuropsychiatrica 19:183 (2007). Table 1, which is not intended to be exhaustive, highlights several applications of CVS.
TABLE 1Disorders/symptoms treated experimentally by CVSDisorder/SymptomTreatedReferenceDizzinessU.S. patent application No. 2003/0195588ElusiveU.S. Pat. No. 6,748,275sleepMigraineO. Kolev, Cephalalgia 10: 167 (1990)headachesNeurodegenerativeY. Yamamoto et al., Ann Neurol. 58: 175 (2005)disordersParkinson'sY. Yamamoto et al., Ann Neurol. 58: 175 (2005)DiseaseReducedU.S. Pat. No. 6,748,275respiratory functionRestrictedU.S. Pat. No. 6,748,275airwaySeasickness/TravelU.S. patent application No. 2003/0195588sicknessSeizureU.S. patent application No. 2003/0195588Spatial- andD. Bachtold et al., Exp Brain Res 136: 128 (2001)verbal-memoryThalamic painV. Ramachandran et al. Neurocase, iFirst,syndrome1-4 (2007)VertigoU.S. Pat. No. 6,748,275;U.S. patent application No. 2003/0195588
CVS activates various areas of the brain that are associated with specific disorders and/or symptoms. Table 2 highlights several such areas of the brain and provides an exemplary listing of some of the disease states/symptoms associated with each area. Without wishing to be bound by any particular theory, it is believed that thermal stimulation of the vestibular system is translated into electrical stimulation within the central nervous system (“CNS”) and propagated throughout the brain, including but not limited to the brain stem, resulting in certain physiological changes that may be useful in treating various disease states (increased blood flow, generation of neurotransmitters, etc). See, e.g., Zhang, et al. Chinese Medical J. 121:12:1120 (2008) (demonstrating increased ascorbic acid concentration in response to cold water CVS). CVS can thus be used to induce serotonin output, ascorbic acid output, acetylcholine release, histamine release, vasopressin release, and/or the production of heat shock proteins with therapeutic value.
TABLE 2Brain areas activated by CVS and disorders/symptomsassociated with each areaBrain AreaActivated by CVSAssociated Disorders/SymptomsBrain stemhiccups, cranial nerve disorders, dizziness,facial weakness, nystagmus, voice alterations,vertical gaze problems, blurredvision, dysarthria, repiratory problemsCerbellumvertigo, nystagmus, tremor, slurred speech,movement disordersCuneus/Precuneusfaulty visual processingFusiform gyrusautism, faulty word/number recognition,faulty processing of color informationHippocampusAlzheimer's disease, memory dysfunctionInsula cortexaddiction, Alzheimer's disease,Parkinson's disease,neurodegenerative disorders,psychiatric disordersLingual gyrusfaulty visual processingParahippocampusfaulty memory encoding/retrievalParietal lobehemianesthesia, seizures, visualdysfunction, facial numbness, agraphia,dysgraphia, alien limb syndrome,spatial neglectPutamenextrapyramidal signsSingular gyrusschizophrenia, ADHD, OCD,mutism, mood disordersSupplementaryseizures, muscle weakness, spasticitymotor cortexTemporal lobeepilepsy, anomia, aphasia, dysphasia,parosmia, anger controlThalamusneuropathic pain, numbness
Methods and devices used to provide CVS may also be used to stimulate cranial nerves within the ear. Activation and/or inhibition of these nerves may be used to treat a wide variety of disorders/symptoms. For example, stimulation of the vagus nerve and/or the trigeminal nerve is often used to moderate pain; and stimulation of the glossopharyngeal, trigeminal, and/or vagal nerves is associated with seizure suppression.
Importantly, pharmacological, electrical and/or electromagnetic nerve stimulation may provide synergistic benefits when combined with thermal stimulation resulting in CVS. The synergistic benefits of combining CVS with electrical or electromagnetic nerve stimulation may be especially prominent when the tissue(s) surrounding the nerve are cooled prior to warming the nerve. Such synergy occurs as a result of the temporal relationship between CVS and cranial nerve activation. Stimulating either the vestibular system or one or more of the cranial nerves leads to cortical activation which does not immediately diminish when the stimulus is removed. If a second stimulus is provided before the previous cortical activation has dissipated, the cortical activation arising from the second stimulus will be enhanced in those areas of the brain that respond to both CVS and cranial nerve stimulation.
For example, if a TED is first used to cool the ear canal and stimulate the subject's vestibular system, a certain level of cortical activation will be achieved (V). If the TED is then used to warm the ear canal and stimulate at least one cranial nerve, a certain level of cortical activation will be achieved (N). If the two stimuli occur close enough in time, the cortical activation resulting from the second stimulus will be enhanced by that fraction of V which has yet to dissipate when the second stimulus occurs (V2), resulting in total cortical activation equal to at least N+V2.
Accordingly, apparatuses and associated methods useful for delivering stimulation to the nervous system and/or the vestibular system of an individual are potentially beneficial to take full advantage of physiological responses that are useful in diagnosing and/or treating a variety of medical conditions.